The invention relates to a method for, making molded parts from several components in plastics processing machines. Preferred field of application of the invention is the production of plastic panes, in particular for the automotive industry.
The manufacture of window panes uses plastic material which becomes brittle after curing. The subsequent separation of the member that is molded on laterally, the so-called sprue, generates, on the one hand, tension in the plastic panes and, on the other hand, particles are released as a consequence of the brittle material and deposit to some extent on the article, so that an unobjectionable product can only be produced by providing additional working steps (washing/drying). In order to fill the cavity as evenly as possible for the large-area molded part, e.g. to prevent streaks, the molding from the side must be implemented with a widest possible sprue. Therefore, the plasticized plastic material is supplied via a manifold with film gating of the cavity. The film gate is realized by configuring the sprue in the form of a slot die.
The invention is now based on the object to obviate the drawbacks associated with the sprue separation, in particular in the case of brittle material.
According to one aspect of the method of the invention, molded parts having several components can be made in a plastics processing machine by providing a sprue element for at least a first component and injecting plasticized plastic material for at least the first component in cavities formed by two mold halves to form a first molded component. While the sprue element of at least the first component remains on the first molded component, plasticized plastic material for at least one additional component is injected in the cavities formed by two mold halves, with the plasticized plastic material for the at least one additional component being molded at least partially around the sprue element. In accordance with the invention, the afore-stated problems are avoided because the sprue separation can now be entirely abolished. Accordingly it is proposed to leave the sprue element on the molded part and to mold around the sprue element in one of the following working cycles.
Embodiments of the invention can include one or more of the following features. The molded part can be a two-dimensional molded part, such as a pane, for example a side pane for an automobile. The sprue can be performed across an edge of the molded part, using at least one manifold and at least one subsequent film gate which can have a cylindrical cross section. The last component of the several components is preferably made of a material that does not substantially release particles during sprue removal. The sprue can be either broken off or cut off. The last component can also be molded on without the sprue element. The second and each additional component can be molded on without the sprue and can include functional elements, such as a strip with holes for attachment to a window lifting mechanism of an automobile has the particular advantage that the sprue element of the first cycle ensures a secure and stable seat of the second part which is molded around, and that functional elements can be provided at the same time in this second part.